1. Field of the Invention
Often in the development of electronic devices there is a requirement for a pulse generator which can produce a square wave output, having a duty cycle (on/off) ratio which can be varied. It is also often necessary that these constant duty cycle ratio generators be capable of operating over a wide input frequency range.
There are many examples of the need for such a frequency constant duty cycle ratio generator such as, for example, the following:
1. In the horizontal deflection circuit of a cathode ray tube display, it is required that the drive transistor be on for 60% and off 40% of the time of each cycle (i.e., 60/40 duty cycle).
2. In electronic ignition systems for combustion engines, it is necessary to provide control of the width of the trigger pulse to eliminate dwell angle sensitivity. To accomplish this, constant duty cycle pulses must be generated over the full engine rpm (frequency) range.
3. In small disc types of digital data storage systems, separate circuits require that sampling apertures be generated for detection of data bits. It is required that these apertures be adjusted as a function of the data rate (held at a constant duty cycle) in order to optimize data recovery.
There are many other examples of areas in which this type of electronic circuitry is required.
2. Description of the Prior Art
In the prior art, there are a number of examples of circuits which provide constant duty cycle outputs at various frequencies. These can provide a present duty cycle over a range of frequencies or a variable duty cycle for a selected small range of frequencies. However, there has not been any which combine the ability to provide an infinitely adjustable duty cycle ratio and simultaneously to adjust to a wide range of frequencies.
A standard flip-flop circuit can provide a 50% duty cycle output over a wide frequency range. However, the disadvantage of these circuits is that they cannot be used to provide other than 50% duty cycle ratio.
Another type of circuit involves the one-shot devices which provide constant duty cycle ratio outputs of other than 50%. The disadvantages of these circuits it that they can be used only for over very limited frequency ranges.
There are other types that involve counters and so forth; however, those circuits are very complex, and they can only provide selected duty cycles and are not adjustable to infinite variations in duty cycle.